Photographic compositions, layers and elements



United States Patent 3,155,519 PHQTQGRAPHIC CQMPGSITIGNS, LAYERS ANDELEMENTS Ralph Kingsley Biake, Westiield, N.J., assignor to E. L du Pontde Nernours and Company, Wilmington, Del., a corporation of Delaware NoDrawing. Filed Oct. 21, 1963, Ser. No. 317,824 12 Claims. (Cl. 96107)This invention relates to photography and more particularly to newimage-yielding photographic silver halide emulsion layers and tophotographic elements embodying such layers.

The present application is a continuation-in-part of my copendingapplication Ser. No. 236,412, filed Nov. 8, 1962.

An object of this invention is to provide new and useful photographicsilver halide layers and elements. Another object is to provide suchlayers which can be used to form direct positives. Yet another object isto provide such layers and elements which cannot be readily fixed duringnormal processing periods prior to exposure. A further object is toprovide such layers which are easy to make, embody relativelyinexpensive chemicals and are dependable in use. Still additionalobjects will be apparent from the following description of theinvention.

The photographic layers and elements, e.g., films, plates and papersembodying such layers, of thi invention comprise, before exposure toactinic radiation, light-sensitive silver halide crystals, preferablyhaving at least by weight of silver chloride, having associatedtherewith in substantially greater than fog-inhibiting amounts, a silvermercaptide of a mercapto compound of the formula wherein R is a hydrogennucleus of 4-12 carbon atoms. Thus, R may be alkyl of 412 carbon atoms,e.g., isobutyl, heptyl and undecyl; cycloalkyl, e.g., cyclohexyl; andaryl, e.g., phenyl. The hydrocarbon nucleus can contain substituentgroups; suitable substituted hydrocarbon radicals include p-bromophenyland p-nitrophenyl. The mercapto compounds can be initially added as thefree SH compound or as the sodium, potassium or ammonium salt.

According to an important and preferred aspect of the invention, R is anunsubstituted hydrocarbon radical of 6l0 carbon atoms and has a cyclichydrocarbon radical of six carbon atoms attached through a cyclic carbonof said radical to the 4-carbon atom of the thiazole ring. Suitableradicals of the latter type include cyclohexyl, methylcyclohexyl,phenyl, tolyl and alpha-naphthyl.

The amount of the silver mercaptide present in the photographic silverhalide layer should be sufficient to protect the silver halide crystalsso that the unexposed layer cannot be fixed by conventional fixingconditions, i.e., at normal times and temperatures and concentrations ofsilver solvent.

In the novel photographic silver halide layers of the invention theprotective silver mercaptide and its concentration relative to thesurface area of the silver halide is characterized in that when testedin a gelatino-silver chloro-bromide emulsion (70% silver chloride and30% silver bromide) which is (a) Applied to a photographic film base ata coating weight of 100 mg./dm. of silver halide and 100 mg./dm. ofgelatin,

(b) Given an exposure of no more than 60,000 metercandle seconds to alight of a color temperature of 2800 K.,

ice

(c) Bathed for 30 seconds at 20 C. in the following solution:

Na2SgO3 (anhyd.) g 100 Na SO (anhyd.) g 9.8 Borax (Na B O -10H O) g 11.8Acetic acid (glacial) ml 7.8 Potassium alum, KAl(SO '12H O g 13.1Potassium acetate g 10 1-1 0 to make 900 ml. Adjust pH to 4.8:01 with 3N H or 3 N NaOH. H O to make 1 liter.

and (d) washed in water for 5 minutes at 20 C. and dried in air,

At least 25 mg./dm. of silver halide remains in the unexposed areaswhile no more than 1 mg./dm. of silver halide remains in the area havingbeen given said exposure.

The silver mercaptide, which is less soluble in water than silverchloride, is further characterized in that when such silver mercaptideis formed by addition of an organic mercaptan or ion thereof to anaqueous dispersion of silver halide, said silver mercaptide protects thesilver halide from solution to the extent that at least three times theamount of silver halide remains undissolved as compared to (a) theuntreated silver halide dispersion or (b) the mercaptan-treated silverhalide dispersion which has subsequently been treated with 5% aqueoussodium hypochlorite, when all three of said dispersions are treatedindividually with equal amounts of 10% aqueous sodium thiosulfate andagitated identically for 30 seconds at 25 C.

Preferably, the silver halide crystals are dispersed in awater-permeable organic colloid to form a light-sensitive photographicsilver halide emulsion. The 4-hydrocarbonsubstituted-Z-mercaptometathiazole can be added to the silver halideemulsion while the latter is in the liquid state or the emulsion may becoated on a suitable support and the resulting element bathed orimpregnated with a solution, e.g., an alcoholic solution of the organiccompound. In the working examples below, the amount of organic compoundin the silver halide emulsion is from about 0.4 to 5 g. per mole ofsilver halide but wider ranges of concentration can be useful, dependingupon the particular organic compound, the size and nature of the silverhalide crystals, the presence of other materials which may partiallycover the surface of the silver halide crystal, and upon various otherfactors.

The gelatin:silver halide ratio is quite flexible and may vary from 3 :1to 1:30 depnding on the particular organic compound and intended use forthe emulsion layer.

In one commercially practical aspect of the invention, the silver halideis present in much higher concentration than in conventional emulsionsand emulsion layers.

In an important use of the products of the invention, direct positiveimages are formed by a process constituting the subject matter of myapplication Ser. No. 236,420 filed Nov. 8, 1962 which process comprisesi (a) Exposing imagewise to actinic radiation a photosensitive layercomprising silver halide crystals treated with an organic compound asdescribed above,

(12) Treating the exposed layer in a solution of a silver halide solventto remove soluble silver halide in the exposed image areas, thus forminga positive silver halide image, and preferably (0) Washing the resultinglayers.

If desired, the silver halide image may be viewed directly, e.g., byprojection (if on a transparent support) or it may be intensified by (d)Converting the residual silver halide to silver by treatment in afogging developer, e.g., a high pH l-phenyl-4-rnethyl-3-pyrazolidone/hydroquinone developer containing iodide ion orby fogging the emulsion by exposure to light and then treating with asilver halide reducing agent, e.g., a conventional silver halidedeveloper, and

(e) Washing the developed layer to reveal a positive silver image in theoriginal non-exposed areas.

The imagewise solution of the exposed silver halide/ organic compoundstratum may be effected by the silver halide solvents commonly used asphotographic fixing agents, e.g., sodium thiosulfate, alkali metalthiocyanate (e.g., sodium, potassium), concentrated solutions ofpotassium bromide, etc. Reduction of the treated, residual silver halidemay be accomplished by use of any chemical reducing agent capable ofreducing silver ion to silver metal, e.g., hydroquinone, metol, sodiumhydrosulfite and stannous chloride. The function of the reducing agentmay be enhanced by modifying the surface propenties of the treated,residual silver halide crystals by means of alcohol, thiourea, potassiumiodide, etc. The silver halide image may be toned, e.g., with sodiumsulfide, sodium selenide, etc. In addition, color images may be obtainedby developing the treated, residual silver halide with a primaryaromatic amine color developing agent in the presence of a colorcoupling compound either in the developing bath or previouslyincorporated in .the emulsion.

The present invention is not limited to a class of organic compoundswith which the silver halide crystals are intimately associated or maybe treated in preparing the novel compositions of this invention. Theutility of a specific 4-substituted-2-mercaptometathiazole compound or asalt thereof can be readily determined by a relatively simple test.Essentially, the test consists of two steps, Test A and Test B. In TestA, the candidate organic compound must render a dispersion of silverhalide crystals insoluble in a silver halide solvent, i.e., an aqueoussolution of sodium thiosulfate, at some pH between 1 and 13. If thecandidate compound meets the insolubility requirements of Test A, itmust also meet the requirements of Test B by forming with saiddispersion of silver halide crystals a reaction product which, upontreatment with an aqueous solution of sodium hypochlorite, becomessoluble when subsequently treated with aqueous sodium thiosulfate. Thefollowing practical tests are provided in further exemplification of theinvention and include specific concentrations of solutions, times, etc.,so that suitable organic compounds may be readily and positivelyidentified.

TEST A A solution nearly saturated at 25 C. with a candidate organiccompound is prepared using ethanol, acetone, dimethyl formamide, wateror other suitable solvents. Depending on the solubility, (a solutionconcentration from 0.01 to 10 percent by weight is obtained. Twentyfiveml. of a silver chlorobromide dispersion containing 25 mg. of silverhalide (calculated as silver bromide), prepared as described below, istreated with small increments (i.e., about 0.1 to 0.2 ml. at a time) ofthe said candidate solution under safelight conditions (Wratten 1Afilter or equivalent) until the silver halide dispersion either isrendered insoluble in 10% aqueous sodium thiosulfate or the candidate isfound not to cause insolubilization. Generally insolubilization willoccur upon the addition of 0.05 g. or less of said candidate compound,calculated as the pure compound. Compounds which must be used insubstantially greater quantities than this, e.g., 1-2 g. to efiectinsolubilization are considered less preferred compounds. The silverhalide dispersion insolubility is determined by taking a 0.5-ml. portionof the silver halide dispersion (after each incremental addition or" thecandidate organic compound), adding about 0.1 to 0.2 ml. of 10% aqueoussodium thiosulfate solution and observing the turbidity afiter 3seconds.

As a control, one should use 25 ml. of water to which small incrementsof the candidate solution are added. Half-milliliter portions of thecontrol are treated in the same manner with the sodium thiosulfatesolution. The

presence of visual turbidity relative to the control is sufficient tosatisfy the definition of insolubility in this test.

This test may be repeated for various pH increments from 1 to 13.Although there is some optimum pH value at which the test is mostsensitive, this is not a sharp maximum which must be precisely attained.Rather, it has been found that there is a fairly broad range of pHvalues (eg 2.0 to 3.0 pH units) over which the test has a satisfactorysensitivity. In practice, the silver halide dispersion might be testedwithout adjustment (e.g. at pH 5.0 to 7.0) and if insolubilizationoccurs here, Test A is completed. If there is no insolubilization, thetest is repeated at a higher pH (e.g., from pH 10-13). If there is stillno insolubilization, the test is conducted with emulsion adjusted to alower pH (e.g., about pH l-3). Thus three different pH values representsa practical maximum number which must be investigated to determinewhether or not insolubilization will occur.

TEST B An organic compound capable of insolubilizing a silver halidedispersion according to Test A is now ready for the next test, whichagain will be conducted under safelight conditions. To the above silverhalide dispersion, there is added the minimum amount of a solution ofthe candidate organic compound found necessary for insolubilization.Half-milliliter samples of the dispersion (containing 0.5 mg. AgBr or0.29 mg. Ag) are placed in two test tubes. To one sample is added 0.5ml. of water; to the other is added 0.5 ml. of a 5% by weight aqueoussolution of sodium hypochlorite (containing 25 mg. sodium hypochlorite).Next, there is added to both samples, 1.0 ml. of an aqueous 10% byweight solution of sodium thiosulfate (containing mg. sodiumthiosulfate). If, after standing for up to thirty seconds, the sampletreated with sodium hypochlorite clarifies (or becomes less turbid)relative to the control sample, the candidate organic compound meets therequirements of Test B and it is satisfactory for use as disclosed inthis invention.

SILVER HALIDE DISPERSION PREPARATION Dispersion I.-The silver halidedispersion disclosed in Tests A and B is prepared according to thefollowing specifications. In red light, 30 g. of photographic gradegelatin is soaked in 1100 ml. of distilled water for 10 minutes. Thetemperature is then raised to F. and 100 g. of solid ammonium chlorideadded. The mixture is stirred at 120 F. and after the ammonium chlorideis completely dissolved, a solution made by diluting 500 ml. of 3 Nsilver nitrate with 2000 ml. of distilled water is added while stirringthe solution for 5 seconds. This mixture is held at 120 F. for 4 minuteswith stirring, and then ml. of 3 N ammonium bromide added (30 molepercent) in 10 seconds. The mixture is held an additional 15 minutes at120 F. with stirring and then cooled to 100 F. A mixture of 75 g. of thesodium salt of technical lauryl alcohol sulfate (a white powder) and 7ml. of 3 N sulfuric acid is added in 10 seconds to the silverchlorobromide, stirring continued for one minute and then the mixtureallowed to settle. The supernatant liquid is decanted and replaced by2000 ml. of distilled water containing 4 g. of sodium chloride. Thismixture is stirred for 5 minutes at 100 F., allowed to settle anddecanted again. Two hundred ml. of distilled water is added to thesilver halide curds and the temperature adjusted to 95 F. This mixtureis vigorously stirred for 10 minutes at 95 F. and then the pH adjustedto 6.1:01 with aqueous sodium hydroxide solution. The redispersedemulsion is then analyzed for silver halide content calculated as silverbromide and a dispersion made by diluting the appropriate amount withdistilled water such that the dispersion contains 1 mg. calculatedsilver bromide per ml.

Dispersed crystals of silver halide, treated with an appropriate amountof a suitable organic compound are affected by exposure of a portion ofsaid crystals to actinic radiation, e.g., ultraviolet, visible,infrared, X- radiation, etc., to such an extent that at least of theless soluble crystals remain when 90% of the more soluble crystalsdissolve when treated in 10% by weight aqueous sodium thiosulfatesolution.

In place of part of the gelatin, other natural or syntheticwater-permeable organic colloid binding agents can be used and in somecases such binders can be used alone. Such agents includewater-permeable or water-soluble polyvinyl alcohol and its derivatives,e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers andacetals containing a large number of intralinear groups, hydrolyzedinterpolymers of vinyl acetate and unsaturated addition polymerizablecompounds such as maleic anhydride, acrylic and methacrylic acid estersand styrene. Suitable such colloids of the last-mentioned type weredisclosed in US. Patents 2,276,322; 2,276,323 and 2,397,866. The usefulpolyvinyl acetals include polyvinyl acetaldehyde acetal, polyvinylbutyraldehyde acetal and polyvinyl sodium o-sulfobenzaldehyde acetal.Other useful colloid binding agents which can be used include thepoly-N-vinyllactams of Bolton US. Patent 2,495,918, variouspolysaccharides, e.g., dextran, dextrin, etc., the hydrophiliccopolymers in Shacklett US. Patent 2,833,650, hydrophilic celluloseethers and esters, and polymers of acrylic and methacrylic esters andamides. Also, it has been found practical to treat silver halide layerson a base material in the essential absence of a binder, e.g., bychemical or vacuum deposition.

The emulsions may optionally contain any of the usual adjuvantscustomarily employed in silver halide systems so long as they do notinterfere with the adsorption and complexing action of the essentialingredient of the invention.

The emulsions can be coated on any suitable support, e.g., celluloseesters, cellulose mixed esters; superpolymers, e.g., polyvinyl chloride(co) vinyl acetate, polyvinyl acetals, butyrals; polystyrene;polyamides, e.g., polyhexamethylene adipamide, polyesters, e.g.,polycarbonates, polyethylene terephthalate, polyethyleneterephthalate/isophthalate, esters formed by condensing terephthalicacid and its derivatives, e.g., dimethyl terephthalate with propyleneglycol, diethylene glycol, tetramethylene glycol,cyclohexane-1,4-dimethanol (hexahydro-p-xylene dialcohol); paper, metal,glass, etc.

As disclosed earlier, the desirable concentration of the selectedorganic compound depends on many factors such as the size and solubilityof the organic compound, the nature of its reaction with silver halide,the size and nature of the silver halide crystals, the presence of othermaterials which may react with or be adsorbed to the surface of thesilver halide, etc. In Example VI of Ser. No. 236,420, a number ofcompounds are disclosed which were tested in a dispersion of silverhalide crystals wherein the average grain size was 0.35 (micron) indiameter, therefore about 0043a in volume, assuming cubic grains. Thesilver halide comprised 70 mole precent silver chloride and mole percentsilver bromide, with a specific density of about 5.7 g./cc. or 5.7 1-0g./,u The weight per individual crystal or grain is 7 Assuming amolecular weight of 157 for the mixed AgCl- AgBr crystals, and dividingthis number by the weight per grain, gives which, multiplied by the 6.3X10 grains per mole, gives a molar surface area of 4.6 10 or 4.6 10square Angstroms.

' A particularly preferred organic compound is2-mercapto-4-phenylthiazole (hereinafter to be referred to as MPT).Assuming that a single molecule of MPT could occupy an area of 28 squareAngstroms, it would require 1.5 10 molecules to occupy a molor surfacearea of silver halide. With a molecular weight of 193, this wouldrequire to just cover the surface of one mole of the silver halidecrystals. In Example VI of Ser. No. 236,420, 1.2 10 g. MPT insolubilized2.5 X 10* g. of silver halide of average molecular weight 157. Thereforeaccording to experimental data (test tube results) it would require toinsolubilize one mole of the silver halide. More significantly, asdisclosed in Example III in a photographic emulsion coated on a filmbase support, it was found that 0.4 g. of MPT per mole of silver halidegave optimum results. This compares more closely with the theoreticallydetermined amount of MPT required to cover the silver halide surface.

As shown in various examples below, e.g. Example I, elements suitablefor this novel process can be prepared by bathing a photographic film ina solution of an appropriate organic compound. In this embodiment, thesilver halide crystals near the surface of the coated emulsion stratumare in contact with a higher concentration of the organic compound.Crystals farther from the surface, are treated with less of the organiccompound and, if the rate of diffusion is sufiiciently slow, there maybe considerably less of the organic compound (even approaching zero)reacting with the lower than with the surface silver halide crystals. Insuch elements, satisfactory results might be obtained with only afraction, e.g., one-half, of the amount of the organic compoundtheoretically calculated as required to just cover the surface of a moleof the silver halide crystals.

With regard to Tests A and B and Dispersion I, by reference to the abovetext or by calculation, it can be readily determined that the2-mercapto-4-hydrocaroon substituted thiazole disclosed herein should bepresent in such an amount, in terms of the ratio of its weight to thesurface area of said silver halide crystals, that when admixed in suchratio with an aqueous silver chlorobromide (70/30 mole percent) gelatinemulsioncontaining 57 g. of gelatin per mole Ag and .57 mg. of Ag/mL,and said silver chlorobromide dispersion is treated with 10%, by weight,aqueous sodium thiosulfate (so that the resulting mixture contains 0.29mg. of silver and mg. of sodium thiosulfate), at least three times theamount of silver chlorobromide remains undissolved as compared with asimilar dispersion successively treated with 5%, by weight, aqueoussodium hypochlorite and 10%, by Weight, aqueous sodium thiosulfate (sothat the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodiumhypochlorite and 100 mg. of sodium thiosulfate), after vigorousagitation of the dispersions for 30 seconds at 25 C.

The invention is useful with silver halide layers free from orcontaining a water-permeable colloid binding agent.

Test C of my prior application, Ser. No. 236,420, can be used todetermine the utility of compounds of this case. According to Test C, a0.5 ml. portion of the insolubilized dispersion of Test A under asafelight is placed in a 12 75 mm. Pyrex test tube 3 inches from a No. 2reflectoflood lamp. This dispersion is exposed to the lamp for up to 10minutes. A control consists of a 0.1 ml. portion of the insolubilizeddispersion from Test A. Two-tenths ml. of 10% aqueous sodium thiosulfateis added to each dispersion and is compared under safelight conditions.Any reduction in turbidity of the dispersion exposed to the lampcompared to the unexposed control after treatment with aqueous sodiumthiosulfate shows that photosolutilization occurs.

The invention will be further illustrated by but is not intended to belimited to the following examples.

Example I A photographic element was prepared by coating an aqueousgelatin dispersion of silver chlorobromide (70 mole percent silverchloride and 30 mole percent silver bromide) on a film base prepared asdescribed in Example IV of Alles US. Patent 2,779,684. The dispersionhad a ratio of silver halide to gelatin of 28:1 by weight and was coatedat a pH of 6 at a rate of 116 milligrams of silver halide per squaredecimeter. After drying, the element was bathed for about 30 seconds inan ethanol-water solution of Z-mercapto-4-phenylthiazole having a pH of5.1 and dried. The solution of 2-mercapto-4-phenylthiazole was preparedby diluting ml. of a stock solution (1 gram of the compound made up to100 ml. in ethanol) with an additional 20 ml. of ethanol and ml. ofwater. The dried element was then exposed behind a photographictransparency for seconds to the radiation from a General Electric 2-Aphotoflood lamp at a distance of about 6-10 inches. The exposed elementwas then immersed in a 12.8% aqueous solution of sodium thiosulfate for30 seconds resulting in removal of the silver salt in the exposed areas.Subsequently, the fixed film was then rinsed briefly in water and bathedin a rapid acting fogging photographic developer solution comprising1-pheny1-4- methyl-3-pyrazolidone and hydroquinone as reducing agents towhich there had been added potassium iodide and a direct positive imageformed. All of the above operations were carried out in ordinaryfluorescent room illumination.

Where a more sensitive product is prepared by appropriate selection ofsuch factors as grain size, silver halide composition, etc., it may bedesirable to use conventional photographic darkroom handling of theelement prior to the image exposure. During the developing step, thetreated element is converted into an exact reproduction (i.e., directpositive image) of the original transparency. After brief washing inwater and drying, it is satisfactory for use in any application where anexact reproduction is desired, e.g., in the graphic arts field, for aprojection transparency, etc.

Example II A photographic element was prepared by coating an aqueousgelatin dispersion of silver bromoiodide (98.86 mole percent silverbromide and 1.14 mole percent silver iodide) on a cellulose acetate filmbase and drying the coating. The dispersion had a ratio of silver halideto gelatin of 1.00:1.03 by weight and was coated at a pH of 6.2 at arate of 105 milligrams of silver halide per square decimeter. Afterdrying, the element was bathed for 30 seconds in a dilute aqueoussolution of Z-mercapto- 4-phenylthiazole and dried. The solution of2-mercapto- 4-phenylthiazole was prepared by diluting 5 ml. of the stocksolution used in Example I with 10 ml. of ethanol and ml. of water, andhad a pH of 4.60. The element was exposed as in Example I except thatthe exposure time was increased to seconds. It was then bathed in thesodium thiosulfate solution of that example for 60 seconds, rinsedbriefly in water, bathed in the same develop for 60 seconds, alloperations being carried out in ordinary fluorescent room illumination.A direct positive image was formed in the same manner as in Example I.The same course of treatment applied to a commercialpanchrornatically-sensitized emulsion gave comparable results.

In connection with the above examples, it has been found that the pH ofthe treating solution used to initially bathe the film has a strikingeffect. With very low pH the effect of the treatment is minimized orcompletely eliminated. For example, with the compound of Example I theeflect of the treatment can be eliminated if the treating solution has apH about 1 or lower. While all of the compounds produce desirableresults over a wide pH range, each compound apparently has an optimum pHrange which is most effective. It will be apparent to one skilled in theart that simple tests can be run to establish the best pH conditions foroperation.

Example 111 A lithographic emulsion having a silver halide compositionof 30 mole percent AgBr and mole percent AgCl and having 20 grams ofgelatin present per mole of silver halide for the steps of precipitationand ripening was freed of unwanted, soluble, byproduct salts by acoagulation and wash procedure as taught in US. Patent 2,489,341,wherein the silver halide and most of the gelatin were coagulated by ananionic wetting agent, sodium lauryl sulfate, using an acid coagulationenvironment. After washing, the emulsion coagulate was redispersed inwater together with 47 g. of additional bulking gelatin per mole ofsilver halide, maintaining a pH of 60:01 while stirring 10 min. at F.Assuming that 10 g. of gelatin was lost during washing, the resultingemulsion contained about 57 g. of gelatin per mole of silver halide. Theemulsion was brought to 2320 g. by addition of water and the temperatureadjusted to F. Four-tenths of a gram of MFT(2-mcrcapto-4-phenylthiazole) was added per mole of silver halide from a1% by weight ethanol solution. Chrome alum hardener was added and theemulsion was diluted with water to a total weight of 2334 g. per mole ofsilver halide. This emulsion was applied at a coating weight of 46 mg.of silver per square decimeter on 0.004 inch thick polyesterphotographic film base as described in Example I. The coating, afterimagewise exposure, showed a greater rate of fixing in a 1.0 N (0.5molar) aqueous sodium thiosulfate in exposed areas than in the unexposedareas so as to form a positive silver halide image. Subsequent flashingto white light, followed by treatment with a reducing agent (aconventional photographic developing solution containing1-phenyl-4-methyl-3 pyrazolidone and hydroquinone), resulted in theformation of a positive image of metallic silver.

Example IV Optical Density Weight of MP1 Uncxposed Heavily ExposedgJmole of silver g./mole of silver g g l mole of silver mole of silver ss m De-HO UIO'IOO Example V A silver bromide emulsion was prepared byadding one mole of 1.5 N AgNO to 1.2 moles of a solution of 0.70 N KBrcontaining 33 g. of gelatin. After ripening 10 minutes at F. theemulsion was coagulated by the addition of a 12% aqueous solution of awater-soluble, acid-soluble partial acetal of polyvinyl alcohol andosulfobenzaldehyde and consisting of 5 g. of sulfonate sulfur per 100 g.of polymer, followed by the addition of sulfuric acid to lower the pH to2.6. An aqueous solution containing 7.2 g. of KBr was then added and thecurds were redispersed at 95 F. for 10 minutes with high shear stirring.Sodium hydroxide was added to adjust the pH to 4.1 and redispersion wascontinued for 30 minutes. The curds were then dispersed in an aqueous16% by weight gelatin solution to give a total of 300 g. gelatin permole of silver bromide. Then 2-mercapto-4-pheny1- thiazole was addedfrom a 1% ethanol solution to give a total of 0.6 g. per mole of silverbromide. The emulsion was adjusted to 2700 g. with water after additionof a chrome alum hardening agent. The emulsion was applied at a coatingWeight of 35 mg. of silver per square decimeter. The coating showed morerapid fixing in an exposed area than in an unexposed area such that uponintensification by subsequent re-exposure and chemical development as inExample 11 a positive metallic silver image was attained with a mixmumoptical density of 1.26 and a minimum optical density of 0.35.

Example VI A silver chloride emulsion was prepared in the same manner asin Example V, except KCl was used instead of KBr at precipitation andredispersion. The KCl at precipitation was present in an amount of 1.08moles per mole of silver nitrate. The curds were dispersed in 17%gelatin to give a total of 94 g. gelatin per mole of silver bromide. MPT(12 mercapto 4 phenylthiazole) was added from a 1% ethanol solution togive a total of 1.0 g. per mole of silver chloride. justed to a finalweight of 1950 g. with Water after the addition of chrome alum as ahardening agent. The emulsion was applied at a coating weight of 35 mg.of silver per square decimeter. The coating showed more rapid fixing inan exposed area such that upon intensification by subsequent re-exposureand chemical development as in Example III a positive metallic silverimage was attained with maximum and minimum optical densities of 1.21and 0.18.

Example VII A silver bromoiodide emulsion of the medical X-ray type wasprepared by adding ammonia converted silver nitrate to a mixture ofammonium bromide and potassium iodide in gelatin. After ripening, theemulsion was coagulation washed. The final emulsion contained 1.6 molepercent silver iodide and 98.4 percent silver bromide. The washed curdswere redispersed in gelatin to give a total of 200- g. of gelatin permole of silver halide. To this emulsion was added 1,3 g. ofZ-mercapto-4-phenylthiazole and the emulsion was applied to the supportdescribed in Example 1 I at a coating weight of 35 mg. of silver persquare decimeter. The coated material showed more rapid fixing in anexposed than in an unexposed area such that upon intensification bysubsequent re-exposure and chemical development as in Example III apositive metallic silver image was attained with maximum and minimumoptical densities of 0.91 and 0.50.

Example VIII A photographic layer was made by evaporating silverchloride onto the film base described in Example I, using a High VacuumEvaporator, Model No. 803 (Optical Film Engineering Co.). The vacuumapparatus employed a tantalum ribbon and operated at a pressure of 3 10microns of mercury. Using about 280 milligrams of AgCl at a distance of24 cm. from the film base, a coating weight of AgCl of about 4 mg./dm.was obtained. The vacuum-coated film was bathed for sec. in theethanol-water (25/10) solution of 2-mercapto-4-phenylthiazole of ExampleI, dried and exposed stepwise for 5, 10, 20, 40 and 80 sec. to aphotoflood lamp (General Electric 2-A) at a distance of 6 inches. Theexposed element was then immersed in 12.8% aqueous sodium thiosulfatefor sec., rinsed in water for 10 sec. and then bathed in a developersolution as described in Example I.

The emulsion was ad- A direct-positive image was formed by the 5 10, 20and 40-second exposures, i.e., imagewise density decreased withincreasing exposure. However, when the exposure was increased to 80sec., a negative image was formed, the system reversing or solarizing byincreased exposure like conventional silver halide systems.

Example IX Example II was essentially repeated except that (a) theelement was bathed for 60 seconds (rather than 30 seconds) in thesolution of 2-mercapto-4-phenylthiazole, (b) the sodium thiosulfatefixing solution was replaced with an aqueous solution containing, on aliter basis, 150 g. KCNS and ml. of 1 molar Na CO and the fixing timewas extended to 2 minutes, and (c) safe lights were used throughout alloperations up to the second treatment with developer solution, withordinary fluorescent room illumination being used subsequently. A directposition image was formed, similar to that of Example II.

Example X A photosoluble element was prepared from a conventionalorthochromatic fully sensitized lithographic gelatino silver halide film(comprising mole percent silver chloride and 30 mole percent silverbromide) having a coating weight of about milligrams per squaredecimeter silver halide. The film support was the same as that describedin Example I. Under safelight conditions, this film was bathed for 30seconds in the dilute ethanolwater solution of2-mercapto-4-phenylthiazole described in Example I. The dried elementwas exposed behind a square-root-of-two photographic step wedge for 10seconds to the radiation from a General Electric 2-A photoflood lamp,operating at 115 volts and at a distance of 6 inches. The exposedelement was then immersed in a 12-18% aqueous solution of sodiumthiosulfate for seconds resulting in removal of the silver salt in theexposed areas. The fixed film was subsequently rinsed briefly in waterand then, under white room lights, bathed in a rapid acting photographicdeveloper comprising 1- phenyl-4-methyl-3-pyrazolidone and thehydroquinone as reducing agents. A direct positive step-wise silverimage formed.

Another sample of the photosoluble element (bathed in the above solutionof 2-mercapto-4-phenylthiazole) was exposed behind a square-root-of-twostep wedge for 3 seconds to the radiation from the above describedphotofiood lamp operating at 25 volts and at a distance of 2 feet.

The exposed element was then developed for 2 minutes at 68 F. in thefollowing conventional photographic developer:

G. Monomethyl-p-aminophenosulfate 3.0 Hydroquinone 9.0 Na sO anhydrous50.0 K CO 50.0 KBr 4.5 Water to make 1 liter.

The film element was then rinsed 15 seconds in running water at 68 F.,fixed 5 minutes at 68 F. in a potassium alum sodium thiosulfate fixingbath (the film required two minutes in the fixing bath to clear), washed10 minutes and dried to give a slow and very weak negative silver image(Negative Image I).

Another sample of the ortho-sensitized litho film (which did not receivethe treatment with /2-mercapto-4-pheny1- thiazole) was exposed,developed, fixed and washed in exactly the same way as just described togive a high speed high density negative image (Negative Image 11). Inthis instance, the film required only 20 seconds in the fixing bath toclear. The optical densities resulting from the positive and twonegative images are given below:

Example XI Four and one-half moles of a ripened and washed emulsion (asdescribed in Example III except for omission of the redispersion step)was mixed with 4 liters of a gelatin solution containing 300 g. ofgelatin. After adjusting the pH to 6.0, the emulsion was redispersed byvigorous agitation for 65 minutes at 110 F. To a quantity of thisredispersed emulsion containing 0.15 mole of silver halide there wasadded 200 ml. of water, an ethanol solution containing 0.1 g. of4-cyclohexyl-2- mcrcaptothiazole and an acetone solution containing 3.5mg. of a merocyanine dye of the structure:

The emulsion was then stirred for 20 minutes at 160 F., cooled to 85 F.,the usual coating adjuvants added, and the emulsion was coated on thefilm base described in Example I.

Example XII The ripened and washed emulsion of Example XI wasredispersed in a similar manner, using 83 g. of gelatin per mole ofsilver halide. To a portion of this emulsion containing 0.15 mole ofsilver halide there was added an ethanol solution containing 0.0625 g.of 2-n1ercapto-4- phenylthiazole. Preparation of the emulsion wascompleted and it was coated as described in Example XI.

Film strips from the coatings of Examples XI-XII were exposed through asquare-root-of-two, neutral density, step wedge to an incandescent lightsource having a color temperature of 2800 K. and an intensity of 6000meter-candles for 10 sec. (total exposure 60,000 m.c.s.).

After exposure the strips were bathed for 20-30 sec. at 20 C. in asolution of the following composition:

N32820:; (anhyd.) g Na SO (anhyd) g 9.8 Borax (Na B O -10H O) g 11.8Acetic acid (glacial) ml 7.80 Potassium alum. KAl(SO -12H O g 13.1Potassium acetate g 10 E to make 900 ml.

Adjust pH to 4.8:01 with 3 N H 80 or 3 N NaOH. H O to make 1 liter Thefilm strips were then washed in water for minutes at 20 C., dried in airand tested by X-ray emission spectrography for silver coating weight, atvarious exposure levels, using a North American Philips X-raySpectrograph Attachment Type No. 52157-A operated from an X-rayDiffraction Unit Type No. 12045. Silver coating weights were alsoobtained in this manner for untreated I 2 control strips of the samecoatings. Results are tabulated below:

Silver Coating Weights (mg/din?) Example Processing Time, sec. UnexposedUnexposed Exposed untreated Treated 10 see.

Treated 20 40.9 22.8 0.35 XII 30 55. 5 29. 8 0. 35

Example XIII A lithographic emulsion having a silver halide compositionof 30 mole percent AgBr and 70 mole percent AgCl and having 20 grams ofgelatin present per mole of silver halide for the steps of precipitationand ripening was freed of unwanted, soluble, by-product salts by acoagulation and wash procedure as taught in Waller et al., US. Patent2,489,341, wherein the silver halide and most of the gelatin werecoagulated by an anionic wetting agent, sodium lauryl sulfate, using anacid coagulation environment. Following the washing step the emulsioncoagulate was redispersed by adding an aqueous solution containing g. ofgelatin per mole of silver halide, adjusting the pH to about 6.0 andvigorously agitating for 65 minutes at 110 F.

To a quantity of this redispersed emulsion containing 0.15 mole ofsilver halide there was added an ethanol solution containing 0.08 gramof 2-mercapto-4-pentylthiazole and an acetone solution containing 3.5mg. of the merocyanine dye of Example XI. The emulsion was then stirredfor 20 minutes at 160 F., cooled to F., the usual coating adjuvantsadded and the emulsion was coated on the film base described in ExampleI, at a silver coating weight of 35 mg./dm. The coating, after imagewiseexposure, showed a greater rate of fixing in an aqueous solutioncontaining 75 g. of sodium thiosulfate per liter in exposed areas thanin the unexposed areas so as to form a positive silver halide image.

Example XIV Example XIII was essentially repeated except the ethanolsolution containing 0.08 gram of 2-mercapto-4- pentylthiazole wasreplaced with an ethanol solution of another Z-mercapto-4-substitutedthiazole in the quantity indicated in the table below. Also, the amountof gelatin per mole of silver halide added at redispersion varied asindicated in the table:

Wt. 01 mercnp- Added Example tan per 0.15 Thiazole substituent gelatinmole of silver at No. 4 position per mole halide, g.

0.07 Il'eptyl 84 0.09 Undeeyl- 84 0.07 Isobutyl 0.12 Alpha-naphthyl...110 0. 12 p-Bromopnenyl. 110 0. 12 p-Nitrophenyl- 110 0.09 p-Diphenyl 84Positive images were obtained from all coatings when tested as inExample XIII.

Example XV Example XIII was essentially repeated except the ethanolsolution containing 0.08 gram of 2-mercapto-4-penty1- thiazole wasreplaced with ml. of an aqueous solution of the sodium salt of2-mercapto-4-phenylthiazole, prepared by dissolving 0.3 gram of2-mercapto-4-phenyl thiazole in 2 ml. of l-molar sodium hydroxide anddiluting with water to a volume of 600 ml. Also, the amount of gelatinper mole of silver halide added at redispersion was 47 grams rather than80 grams. When tested as in Example XIII, the results were similar, apositive image being obtained from this coating.

The 2-mercapto-4-pentyl-, heptyl, undecyl, etc. thiazole compounds canbe prepared by procedures like those for making lower homologues andanalogues. Thus, they can be made by the procedures of Ritter et al., J.Am. Chem. Soc., vol. 70, pp. 3419-21, from NH CSSNH and the appropriateN-alkyl chloromethyl ketone, etc.

When the sodium, potassium or ammonium salt is used in place of the freemercaptan, there are advantages as these salts can be added from aqueoussolution instead of from an ethanol solution.

The silver halide photosoluble elements of this invention differ fromconventional silver halide emulsions containing antifogging agents inthat the insolubilizing compounds used in the photosoluble elements arepresent in substantially greater than fog-inhibiting amounts, the latteramounts being the maximum quantity which provides low fog withoutserious loss in speed and photographic quality. For this reason it isnot practical to use photosoluble elements in place of ordinary silverhalide photograpmc materials. When photosoluble elements are exposed andprocessed normally, development proceeds slowly and incompletely to givea negative silver image having much less speed and lower density. Inaddition, 1 .ing is slower and may be incomplete for practical fixingtimes. Thus, photosoluble elements require longer conventionalprocessing times and give slower speed, inferior quality images whencompared to ordinary silver halide photographic elements.

The novel photographic products of this invention have numerousadvantages. A primary advantage is the simplicity of their preparation.They can be exposed and processed to images under ordinary room lightconditions.

The photographic processes applicable to the new products of theinvention likewise have advantages over previously known systems basedon selective reduction of exposed silver halide for forming eitherdirect positive or negative images Without resorting to the specialeffects and sensitizing procedures previously used for preparing suchimages. in addition, since image formation does not re quire selectivereduction, this present process is not limited to the use of certainphotographic developing agents but may be accomplished by using a widerange of reducing agents. Many such compounds are of very low cost andcan be used to form images of much higher covering power than customary,thus elfecting important economies in processing, as well as greatlyincreasing the efiiciency of the silver image with a resultant increasein sensitivity.

Another advantage of this invention is that it provides new elements forforming silver images that do not require special equipment but insteadcan be used with conventional equipment and apparatus. A furtheradvantage is that the elements can be used successfully by photographictechnicians and photographers of ordinary skill. A still furtheradvantage is that the elements can be processed with conventionalreducing agents, e.g., developers and fixing agents. A still furtheradvantage is that the new elements can be used to produce images withoutselective reduction.

I claim:

1. A photographic silver halide emulsion layer wherein any heavy metalsalt present is a silver halide comprising, before exposure to actinicradiation, light-sensitive silver halide crystals having associatedtherewith in substantially greater than fog-inhibiting amounts a silvermercaptide of a mercapto compound of the formula:

where R is a hydrocarbon nucleus of 4-12 carbon atoms, said silvermercaptide being of lower solubility in Water than silver chloride andthe silver halide crystals so associated with the silver mercaptidedissolving more slowly in aqueous sodium thiosulfate than untreatedsilver halide crystals at a predetermined pH, the mercapto compoundforming the mercaptide being present in such an amount, in terms of theratio of its Weight to the surface area of said silver halide crystals,that when admixed in such ratio with an aqueous silver chlorobromide(70/30 mole percent) gelatin dispersion containing 57 g. of gelatin permole Ag and .57 mg. of Ag per ml., and said silver chlorobromidedispersion is treated with 10%, by weight, aqueous sodium thiosulfate(so that the resulting mixture contains 0.29 mg. of silver and mg. ofsodium thiosulfate), at least three times the amount of silverchlorobromide remains undissolved as in a similar dispersionsuccessively treated with 5%, by weight, aqueous sodium hypochlorite and10%, by Weight, aqueous sodium thiosulfate (so that the resultingmixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and100 mg. of sodium thiosulfate), after vigorous agitation of thedispersions for 30 seconds at 25 C.

2. An emulsion layer according to claim 1 wherein said emulsion layercontains gelatin as the binding agent for the crystals.

3. An emulsion layer according to claim 1 wherein the silver halide issilver chlorobromide.

4. A photographic silver halide emulsion layer wherein any heavy metalsalt present is a silver halide comprising, before exposure to actinicradiation, light-sensitive silver halide crystals having associatedtherewith in substantially greater than fog-inhibiting amounts a silvermercaptide of a mercapto compound of the formula:

Where R is an unsubstituted hydrocarbon radical of 6-10 carbon atomshaving a cyclic hydrocarbon radical of six carbon atoms attached througha cyclic carbon atom thereof to the 4-carbon atom of the thiazole ring,said silver mercaptide being of lower solubility in water than silverchloride and less soluble in 10% aqueous sodium thiosulfate thanuntreated silver halide crystals at a predeter-' mined pH, said mercaptocompound forming the mercap tide being present in such an amount, interms of the ratio of its weight to the surface area of said silverhalide crystals, that when admixed in such ratio with an aqueous silverchlorobromide (70/30 mole percent) gelatin dis persion containing 57 g.of gelatin per mole Ag and .57 mg. of Ag/ml. and said silverchlorobromide dispersion is treated with 10%, by Weight, aqueous sodiumthiosulfate (so that the resulting mixture contains 0.29 mg. of silverand 100 mg. of sodium thiosulfate), at least three times the amount ofsilver chlorobromide remains undissolved as in a similar dispersionsuccessively treated with 5%, by weight, aqueous sodium hypochlorite and10%, by weight, aqueous sodium thiosulfate (so that the resultingmixture contains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and100 mg. of sodium thiosulfate), after vigorous agitation of thedispersions for 30 seconds at 25 C.

5. An emulsion layer according to claim 4 wherein R is phenyl.

6. An emulsion layer according to claim 4 wherein R is phenyl, thesilver halide is silver chlorobromide and gelatin is present as thebinding agent for the silver chlorobromide.

7. An emulsion layer according to claim 4 wherein R is cyclohexyl.

8. An emulsion layer according to claim 4 wherein R is cyclohexyl, thesilver halide is silver chlorobromide and gelatin is present as thebinding agent for the silver chlorobromide.

9. A photographic silver halide emulsion layer wherein any heavy metalsalt present is a silver halide comprising, before exposure to actinicradiation, light-sensitive silver halide crystals having associatedtherewith in substantially greater than fog-inhibiting amounts a silvermercaptide of a mercapto compound, said silver mercaptide and itsconcentration relative to the surface area of the silver halide ischaracterized in that when tested in a gelatino-silver chlorobromideemulsion (70% silver chloride and 30% silver bromide) which is (a)applied to a photographic film base at a coating weight of 100 mg./dm.of silver halide and 100 mg./dm. of gelatin,

(b) given an exposure of no more than 60,000 meter candle-seconds to alight of a color temperature of 2800 K.,

(c) bathed for 30 seconds at C. in the following solution:

Na S O (anhyd.) g 100 Na SO (anhyd.) g 9.8 Borax (Na B O 10H O) g 11.8Acetic acid (glacial) ml 7.8 Potassium alum, KAl(SO -12H O g 13.1Potassium acetate g 10.0

H 10 to make 900 ml. Adjust pH to 4.8i0.1 with 3 N H 80 or 3 N NaOH. H Oto make 1 liter and (d) washed in water for 5 minutes at 20 C. and

dried in air, at least mg./dm. of silver halide remains in the unexposedareas while no more than 1 n1g./drn. of silver halide remains in thearea having been given said exposure. 10. A photographic silver halidecomposition wherein any heavy metal salt is a silver halide comprising,before exposure to actinic radiation, light-sensitive silver halidecrystals having associated therewith in substantially greater thanfog-inhibiting amounts a silver mercaptide of a mercapto compound of theformula:

II It HC o-srr where R is a hydrocarbon nucleus of 4-12 carbon atoms,said silver mercaptide being of lower solubility in water than silverchloride and the silver halide crystals so associated with the silvermercaptide dissolving more slowly in 10% aqueous sodium thiosulfate thanuntreated silver halide crystals at a predetermined pH, the mercaptocompound forming the mercaptide being present in such an amount, interms of the ratio of its Weight to the surface area of said silverhalide crystals, that when admixed in such ratio with an aqueous silverchlorobromide (70/ mole percent) gelatin dispersion containing 57 g. ofgelatin per mole Ag and .57 mg. of Ag per ml., and said silverchlorobromide dispersion is treated with 10%, by weight, aqueous sodiumthiosulfate (so that the resulting mixture contains 0.29 mg. of silverand 100 mg. of sodium thiosulfate), at least three times the amount ofsilver chlorobromide remains undissolved as in a similar dis persionsuccessively treated with 5%, by weight, aqueous sodium hypochlorite and10% by weight, aqueous sodium thiosulfate (so that the resulting mixturecontains 0.29 mg. of silver, 25 mg. of sodium hypochlorite and 100 mg.of sodium thiosulfate), after vigorous agitation of the dispersions for30 seconds at 25 C.

11. A photographic silver halide emulsion layer comprising, beforeexposure to actinic radiation, light-sensitive silver halide crystalshaving associated therewith in substantially greater than fog-inhibitingamounts, and from one-half the amount required to just cover the surfaceof a mole of the silver halide crystals to 0.75 gram per mole of saidcrystals of 2-mercapto-4-phenylthiazole, said compound thereby beingpresent in such an amount, in terms of the ratio of its Weight to thesurface area of said silver halide crystals, that when admixed in suchratio with an aqueous silver chlorobromide 30 mole percent) gelatindispersion containing 57 g. of gelatin per mole Ag and .57 mg. of Ag perml., and said silver chlorobromide dispersion is treated with 10%, byweight, aqueous sodium thiosulfate (so that the resulting mixturecontains 0.29 mg. of silver and mg. of sodium thiosulfate), at leastthree times the amount of silver chlorobromide remains undissolved as ina similar dispersion successively treated with 5%, by weight, aqueoussodium hypochlorite and 10%, by weight, aqueous sodium thiosulfate (sothat the resulting mixture contains 0.29 mg. of silver, 25 mg. of sodiumhypochlorite and 100 mg. of sodium thiosulfate), after vigorousagitation of the dispersions for 30 seconds at 25 C.

12. An emulsion layer according to claim 11 wherein the silver halide issilver chlorobromide and gelatin is present as the binding agent for thesilver chlorobromide.

References Cited by the Examiner Mees: The Theory of the PhotographicProcess"; Macmillan, 1942, pages 306-309 of interest.

Faerman et al.: The Photographic Action of 2-Mercapto Benzoxazide,Uspekhi Nauchonoi Fotografii, Akademiya Nauk, S.S.S.R., OtdelenieKhimicheskikh Nauk 5, 107-113 (1957).

Van Veelen et al.: Phot. Korr. 99, No. 9, September 1963, pages 139-145of interest.

NORMAN G. TORCHIN, Primary Examiner.

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION LAYER WHEREIN ANY HEAVY METALSALT PRESENT IS A SILVER HALIDE COMPRISING, BEFORE EXPOSURE TO ACTINICRADIATION, LIGHT-SENSITIVE SILVER HALIDE CRYSTALS HAVING ASSOCIATEDTHEREWITH IN SUBSTANTIALLY GREATER THAN FOG-INHIBITING AMOUNTS A SILVERMERCAPTIDE OF A MERCAPTO COMPOUND OF THE FORMULA: